1. Field of the Invention
The invention relates to a single wafer type substrate cleaning method and a single wafer type substrate cleaning apparatus, more particularly to a single wafer type wet-cleaning technique or system for applying a cleaning treatment to substrates such as semiconductor wafers one by one during the fabrication process of semiconductors and devices such as electronic parts and the like.
2. Prior Art
A so-called batch type wet cleaning system has been the principal method of cleaning substrates such as semiconductor wafers (hereinafter referred to simply as xe2x80x9cWafersxe2x80x9d), whereby waters stored in a carrier cassette are immersed in sequence in wet bench type cleaning baths arranged in series, or wafers are directly immersed in the baths through a transfer unit without being stored in the carrier cassette. However, semiconductor devices have reached the sub micron age, in that they are now micro-fabricated and highly integrated, such that the face of wafers has recently required a very high degree of cleaning density, and wafers which are not stored in a cassette have to be wet-cleaned individually in a sealed cleaning housing. To this end, a so-called single wafer type wet cleaning system intended to meet the requirement of a higher cleaning density has been developed and proposed. The present applicant has improved this single wafer type wet cleaning method, and filed Japanese Patent Application No. 2000-370718 for such improvement. The said invention relates to a method for effectively preventing oxidation on the front faces of wafers while optimizing the benefits of the single wafer type substrate wet-cleaning system for cleaning wafers, individually, which are not stored in a cassette, in a sealed cleaning chamber.
Under the single wafer type wet cleaning system, wafers can be cleaned with the use of a simple and compact cleaning apparatus in a relatively clean atmosphere where particles and the like do not settle or remain on the face of the wafer. This system is therefore practical to use for small scale production.
Generally, under the single wafer type wet cleaning system, the front face, i.e., the upper side surface of the wafer, is cleaned by the application of various chemical fluids in a predetermined order, and recently, a technique whereby both the front and back faces of wafers can be simultaneously cleaned has also been developed. Basically, the back face i.e., the lower side surface of the wafer, is cleaned by the injection and supply of chemical fluids from the lower side surface to the upper side surface of the wafer, giving rise to the probability of cross contamination of the wafer by the different chemical fluids between cleaning treatments. The present invention therefore seeks to address this problem of cross contamination.
The object of the invention is to provide a single wafer type wet cleaning technique capable of simultaneously wet cleaning the front and back faces of wafers, individually, which are not stored in a cassette, in a sealed cleaning chamber.
To achieve this object, the proposed invention comprises a single wafer type cleaning method for wet-cleaning wafers, individually, which are not stored in a cassette, in a sealed cleaning housing, whereby the front and back faces of each wafer, which is rotatably supported in the cleaning housing, are vertically and sequentially supplied with various chemical fluids from upper and lower side supply nozzles and purified water is always made to flow out of at least one of the lower side supply nozzles which does not supply any chemical fluid.
In the preferred embodiment, the single wafer type substrate cleaning method further comprises a rinsing treatment of each wafer by supplying purified water from the upper and lower side supply nozzles which supply chemical fluids between cleaning treatments and a cleaning treatment by supplying various other chemical fluids in another series of cleaning treatments, and by causing purified water to continuously flow out of at least one of the lower side supply nozzles upon completion of the rinsing treatment. In this case, it is preferable that the flow of the purified water from the lower side supply nozzle shall be of minimum velocity to prevent the counter flow of chemical fluids other than the chemical fluids supplied from the lower side supply nozzles.
Further, the single wafer type substrate wet-cleaning apparatus of the invention is suitable for carrying out the foregoing cleaning method and comprises (1) wafer rotary means for supporting and rotating a single wafer in the cleaning housing in the horizontal position, (2) a cleaning chamber provided at the outer peripheral portion of the wafer rotary means for forming a cleaning treatment space for cleaning the wafer which is rotatably supported by the wafer rotary means, and (3) chemical fluid supply means for supplying chemical fluids to the front and back faces of the wafer which is rotatably supported by the wafer rotary means, wherein the chemical fluid supply means is provided in the cleaning housing and consists of upper side supply nozzles for supplying chemical fluids to the front face of the wafer from the upper side of the cleaning housing and lower side supply nozzles for supplying the chemical fluids to the back face of the wafer from the lower side thereof, and wherein the upper and lower side supply nozzles vertically and sequentially supply a plurality of chemical fluids to the front and back faces of the wafer which is rotatably supported by the wafer rotary means, thereby cleaning the wafer, and purified water is always made to flow out of the lower side supply nozzles which do not supply chemical fluids, of the lower side supply nozzles, in a series of cleaning steps.
In the preferred embodiment, the upper and lower side supply nozzles are composed of injection nozzles for injecting and supplying the chemical fluids to the front and back faces of each wafer which is rotatably supported by the wafer rotary means, and the number of supply nozzles employed depends on the kind of chemical fluids to be supplied. Further, the lower side supply nozzles are directed upward and located on the upper end portion of the rotatable rotary shaft of the wafer rotary means, and they can communicate with either the chemical fluid supply source or the purified water supply source.
Notably, it is preferable that a gap is established between the inner periphery of the rotary shaft of the wafer rotary means and the outer periphery of the pipe to serve as a supply port of inert gas.
Under the single wafer type cleaning system of the invention, wafers which are not stored in a cassette, are individually cleaned in the sealed cleaning housing, by vertically and sequentially supplying various chemical fluids from the upper-and lower supply nozzles to the front and back faces of each wafer which is rotatably supported by the wafer rotary section.
In this case, purified water is always caused to flow out of the lower side supply nozzles which do not supply chemical fluids, of the lower side supply nozzles, in order that cross contamination of such chemical fluids can be prevented between cleaning treatments of the wafers.
In detail, when chemical fluids are supplied to the back face of each wafer from the lower side to the upper side, some of the chemical fluids are prone to remain in the lower side supply nozzles as the lower side supply nozzles are constructed in such manner as to be opened upward. Accordingly, when the cleaning treatment is effected by another chemical fluid upon completion of the cleaning treatment by a particular chemical fluid, the chemical fluid remaining in the lower side supply nozzles in the preceding cleaning treatment(s) mixes with other chemical fluids in the succeeding cleaning treatments, or, chemical fluids supplied between cleaning treatments enter the lower side supply nozzle 26 which is on standby so that such chemical fluids mix with a different kind of chemical fluid remaining in the standby supply nozzle 26, giving rise to a high probability of cross contamination of the chemical fluids between cleaning treatments.
In consideration of the foregoing problem, according to the invention, purified water is always made to flow out of the lower side supply nozzles which do not supply chemical fluids, of the lower side supply nozzles, so that the anticipated occurrence of cross contamination of various chemical fluids between cleaning treatments can be avoided.
Under the single wafer type substrate cleaning system of the invention, a plurality of chemical fluids are sequentially supplied from the upper and lower supply nozzles to the front and back faces of each wafer which is rotatably supported by the wafer rotary means such that each wafer, which is not stored in a cassette, is wet-cleaned in the sealed cleaning housing, wherein purified water is always made to flow out of the lower side supply nozzles which do not supply chemical fluids, of the lower side supply nozzles, so that cross contamination of various chemical fluids between cleaning treatments can be prevented.
In other words, when the supply of chemical fluids to the back face of each wafer is effected from the lower side to the upper side, the chemical fluids which are prone to remain in the lower side supply nozzles because of the upward manner in which they are constructed mix with other chemical fluids supplied between cleaning treatments upon completion of each cleaning treatment by one chemical fluid, as would lead to cross contamination of such chemical fluids. According to the invention, therefore, it is possible to effectively prevent the occurrence of cross contamination of various chemical fluids between cleaning treatments by causing purified water to flow out of the lower side supply nozzles which do not supply chemical fluids, of the lower side supply nozzles.